Surface emitting laser array, production process thereof, and image forming apparatus having surface emitting laser array

ABSTRACT

A surface emitting laser array comprising a plurality of surface emitting laser devices each having a semiconductor layer containing a first reflection mirror, an active layer, a current confined portion and a second reflection mirror. The laser array further comprises a first metal material layer for dissipating heat formed through a first insulating layer on the semiconductor layer and a second metal material layer for injecting current into the active layer formed through a second insulating layer on the first metal material layer. The first metal material layer is commonly shared by the plurality of the surface emitting laser devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface emitting laser array, aproduction process thereof, and an image forming apparatus having asurface emitting laser array.

2. Description of the Related Art

A vertical cavity surface emitting laser (VCSEL) is a laser capable ofemitting light in a direction perpendicular to a substrate surface andhas a feature that a two-dimensional array can be easily formed, whichan edge-emitting type laser does not have.

In particular, densification and faster operation can be simultaneouslyachieved by the parallel processing of multiple beams emitted from thetwo-dimensional array, and so it is expected to be used in variousindustrial applications. For example, when a vertical cavity surfaceemitting laser array is used as a light source for exposure ofelectrophotography, high-definition and faster printing can be achievedby parallel processing in a printing process by utilizing multiplebeams.

On the other hand, the vertical cavity surface emitting laser involves aproblem that saturation of light output is caused by temperature risecaused by generation of heat upon low-current driving compared with theedge-emitting type laser, and so the light output is limited.

In addition, the vertical cavity surface emitting laser also involves aproblem that light output is lowered with rise of a peripheraltemperature (environmental temperature) of a device.

In order to solve such problems, Japanese Patent Application Laid-OpenNo. 2003-086895 has proposed a vertical cavity type semiconductorlight-emitting device in which a peripheral part of a mesa structure ischarged with a plated metal to dissipate heat as well as to impart afunction as an electrode.

When an array type vertical cavity surface emitting laser is applied toa light source for electrophotography, the distance between verticalcavity surface emitting laser devices is more and more shortened fromdemands such as faster operation and high definition, and there is ademand for more narrowing the pitch between the devices.

When peripheral parts of a mesa structure of such a narrow-pitch laserare charged with a plated metal like Japanese Patent ApplicationLaid-Open No. 2003-086895, thereby forming plated structures which takea radiator function as a heat sink part, the plated structures come intocontact with each other, so that the devices are difficult to beindependently driven.

On the other hand, in order to independently drive the devices, it isalso considered that a plating-formation-inhibiting portion is formed asa device-isolating structure between the narrow-pitch devices. When sucha device-isolating structure is formed, however, it is difficult toallow the area of the plated structure having the radiator function tobe large.

As described above, it is difficult to achieve both independent drive ofthe respective devices and efficient heat dissipation when the distancebetween the devices is narrow in the prior art.

SUMMARY OF THE INVENTION

In view of the above-described problems, it is thus an object of thepresent invention to provide a surface emitting laser array that canefficiently perform heat dissipation and independently drive the deviceseven when the distance between the devices is narrow, and a productionprocess of the array. Another object of the present invention is toprovide an image forming apparatus using the laser array according tothe present invention.

The present invention provides a surface emitting laser array comprisinga plurality of surface emitting laser devices each having asemiconductor layer containing a first reflection mirror, an activelayer, a current confined portion and a second reflection mirror, whichfurther comprises a first metal material layer for dissipating heatformed through a first insulating layer on the semiconductor layer and asecond metal material layer for injecting current into the active layerformed through a second insulating layer on the first metal materiallayer, wherein the first metal material layer is commonly shared by theplurality of the surface emitting laser devices.

The present invention also provides an image forming apparatuscomprising the surface emitting laser array.

The present invention further provides a process for producing a surfaceemitting laser array comprising a semiconductor layer having a firstreflection mirror, an active layer, a current confined portion and asecond reflection mirror, the process comprising the steps of: etchingthe semiconductor layer to form a mesa structure; forming a firstinsulating layer on the semiconductor layer; forming a first metalmaterial layer for dissipating heat on the first insulating layer so asto cover side regions of the active layer; forming a second insulatinglayer on the first metal material layer; and forming a second metalmaterial layer for injecting current into the active layer on the secondinsulating layer.

According to the present invention, it is possible to realize a surfaceemitting laser array that can efficiently perform heat dissipation andindependently drive the devices even when the distance between thedevices is narrow. The production process of the surface emitting laserarray according to the present invention can also be realized. The imageforming apparatus having the surface emitting laser array according tothe present invention can further be realized.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 1A schematically illustrate a vertical cavity surfaceemitting laser array in Example 1 of the present invention.

FIGS. 2A, 2B, 2C, 2D, 2E, 2F and 2G schematically illustrate aproduction process of the vertical cavity surface emitting laser arrayin Example 1 of the present invention.

FIGS. 3 and 3A schematically illustrate a vertical cavity surfaceemitting laser array in Example 2 of the present invention.

FIGS. 4A, 4B, 4C, 4D, 4E, 4F and 4G schematically illustrate aproduction process of the vertical cavity surface emitting laser arrayin Example 2 of the present invention.

FIGS. 5A and 5B schematically illustrate structural drawings of an imageforming apparatus of an electrophotographically recording system, inwhich a vertical cavity surface emitting laser array in Example 3 of thepresent invention is mounted.

DESCRIPTION OF THE EMBODIMENTS

In an embodiment of the present invention, surface emitting laserdevices each having a semiconductor layer containing a first reflectionmirror, an active layer, a current confined portion and a secondreflection mirror are used to constitute a vertical cavity surfaceemitting laser array in the following manner.

Upon the constitution of the vertical cavity surface emitting laserarray in this embodiment, a first metal material layer for dissipatingheat and a second metal material layer for injecting current into theactive layer are respectively individually provided for efficientlydissipating heat generated and enabling independent drive.

Specifically, the first metal material layer is comprised of a metalmaterial layer for heat dissipation and is so arranged as to cover apart of a mesa structure (particularly, so as to surround an activelayer region) through a first insulating layer on the semiconductorlayer.

The second metal material layer is comprised of a metal material layerfor wiring, and a second insulating layer is inserted between the metalmaterial layer for heat dissipation and the metal material layer forwiring so that these material layers are not electrically connected toeach other.

The metal material layer for heat dissipation, which functions as aradiator, is commonly shared by the respective devices.

By the above-described constitution, the respective devices can beindependently driven without being electrically connected to each otherand heat can be efficiently dissipated even when the vertical cavitysurface emitting laser array is narrow in pitch. In particular, there isno need to individually form a metal material layer for heat dissipationat every device like the prior art, and the metal material layer forheat dissipation, which functions as a radiator, can be commonly sharedby the respective devices, so that the metal material layer can beformed as a heat sink having a large area to more efficiently conductheat dissipation.

An image forming apparatus having the vertical cavity surface emittinglaser array having the effect of the present invention is constituted,whereby an image forming apparatus capable of realizing high-speed andhigh-definition printing can be obtained.

The present invention will hereinafter be described by the followingExamples.

Example 1

In Example 1, a structural example of a vertical cavity surface emittinglaser array constituted by applying the present invention is described.

FIGS. 1 and 1A illustrate a vertical cavity surface emitting laser arrayaccording to this embodiment. FIG. 1A is a cross-sectional view takenalong line 1A-1A in FIG. 1. A plurality of surface emitting laserdevices is arranged in this surface emitting laser array.

In FIGS. 1 and 1A, a semiconductor layer 100 contains at least a firstreflection mirror, an active layer, a current confined portion and asecond reflection mirror, which are formed on a substrate.

In this embodiment, the first reflection mirror is comprised of a DBRmirror. In this embodiment, a first metal material layer is comprised ofa metal material layer for heat dissipation indicated by ‘102’.

The laser array comprises a first insulating layer 104, a secondinsulating layer 106, the active layer 108, a metal material layer 110for wiring and an electrode 112.

In the vertical cavity surface emitting laser array according to thisembodiment, the first insulating layer 104 is formed on thesemiconductor layer 100 at portions other than the top surface of a mesastructure which is so formed that the DBR mirror layer is exposed. Inother words, the first insulating layer 104 is formed on thesemiconductor layer except on laser emission ports formed on the upperlayer side of the second reflection mirror.

The metal material layer 102 for heat dissipation is formed over thesemiconductor layer 100, on which the first insulating layer 104 isformed, so as to cover them including side portions of the active layer108.

The second insulating layer 106 is formed on at least other portions ofthe metal material layer for heat dissipation than the upper surface ofthe mesa structure.

The metal material layer 110 for wiring is formed on the secondinsulating layer 106.

According to such construction of this embodiment, the metal materiallayer 102 for heat dissipation and the metal material layer 110 forwiring can be formed being isolated by the insulating layer, so that thedevices can be independently driven.

Since the metal material layer for heat dissipation can be commonlyshared by the devices, heat can be more efficiently dissipated than thecase where a metal portion for heat dissipation is formed at everydevice like the prior art. When the thickness of each metal materiallayer for heat dissipation is controlled to such a thickness that awiring by the metal material layer for wiring is not broken by a leveldifference, the disconnection of the wiring can be inhibited.

The production process of the vertical cavity surface emitting laserarray according to this embodiment will hereinafter be described.

FIGS. 2A to 2G are typical drawings illustrating the production processof the surface emitting laser array according to this embodiment.

In FIGS. 2A to 2G, an n-type GaAs substrate 200, a semiconductor epilayer 202, an active layer 204, a mesa structure 206, a first insulatinglayer 208, a metal material layer 210 for heat dissipation, a secondinsulating layer 212, a metal material layer 214 for wiring and anelectrode metal layer 216 are illustrated.

In this embodiment, the vertical cavity surface emitting laser array isproduced through the following respective steps.

First, as illustrated in FIG. 2A, the semiconductor epi layer 202 isgrown on the n-type GaAs substrate 200 through a buffer layer in thefollowing manner by an MOCVD system. More specifically, an n-typeAl_(0.9)Ga_(0.1)As/Al_(0.12)Ga_(0.88)AS-DBR mirror layer, an n-typeAl_(0.6)Ga_(0.4)As spacer layer, and a GaAs/Al_(0.3)Ga_(0.7)As-MQWactive layer 204 are successively grown. Further, a p-typeAl_(0.6)Ga_(0.4)As spacer layer, a p-type Al_(0.98)Ga_(0.02)As layer, ap-type Al_(0.9)Ga_(0.1)As/Al_(0.12)Ga_(0.88)AS-DBR mirror layer and ap-type GaAs contact layer are then successively grown.

As illustrated in FIG. 2B, the mesa structure 206 is then formed bymeans of lithographic and dry etching techniques so as to expose then-type Al_(0.9)Ga_(0.1)As/Al_(0.12)Ga_(0.88)AS-DBR mirror layer.Incidentally, it is also applicable to only conduct etching to theGaAs/Al_(0.3)Ga_(0.7)As-MQW active layer 204 from the viewpoint ofdevice isolation.

As illustrated in FIG. 2C, a first insulating layer (silicon oxide film)208 is then formed at other portions than the top surface of the mesastructure by means of CVD film-forming, lithographic and etchingtechniques.

As illustrated in FIG. 2D, a metal material (Ti/Au) layer 210 for heatdissipation is then formed to a thickness of 3 μm on the firstinsulating layer by means of lithographic and metal depositiontechniques so as to cover side regions of the active layer 204.

As illustrated in FIG. 2E, a second insulating layer 212 is then formedon at least other portions of the metal material layer for heatdissipation than the upper surface of the mesa structure by means of CVDfilm-forming, lithographic and etching techniques.

As illustrated in FIG. 2F, a metal material (Ti/Au) layer 214 for wiringfor device-driving is then formed to a thickness of 1 μm on the secondinsulating layer by means of lithographic and metal depositiontechniques.

As illustrated in FIG. 2G, an electrode metal (AuGe/Au) layer 216 isthen formed on the n-type GaAs substrate 200 by means of a metaldeposition technique.

By the steps described above, the vertical cavity surface emitting laserarray in which the metal material layer for efficiently dissipating heatgenerated in the active layer of the surface emitting laser and themetal material layer that is wiring for driving the surface emittinglaser are individually formed can be obtained.

Incidentally, a 4×4 vertical cavity surface emitting laser array havinga mesa diameter of 20 μm and a mesa pitch of 40 μm is formed in thisembodiment. In this embodiment, the metal material layer for heatdissipation having a thickness of 2.5 μm from the center of the activelayer is formed by deposition.

The thickness of the metal material layer for heat dissipation iscontrolled in such a manner that a height from the top of the mesastructure to the outermost surface of the metal material layer for heatdissipation is 2 μm or less. By taking such construction, the metalmaterial layer for wiring can be formed without disconnection.Incidentally, if the height from the top of the mesa structure to theoutermost surface of the metal material layer for heat dissipationexceeds 2 μm, the frequency of disconnection becomes high.

In an m×n (m and n: natural numbers exclusive of 0) vertical cavitysurface emitting laser array having a pitch of 80 μm or less betweensurface emitting laser devices according to this construction, thefollowing advantage can be obtained. More specifically, the metalmaterial layers for heat dissipation and for wiring are isolated fromeach other (a layered structure is taken with an insulating layerinserted between these layers), whereby the degree of freedom of wiringpattern can be increased. In addition, a narrow-pitch, two-dimensionalvertical cavity surface emitting laser array that can inhibitdisconnection and efficiently dissipate heat generated in the activelayer can be produced.

Although the 850-nm band vertical cavity surface emitting laser has beendescribed in this embodiment, the present invention is not limited tothis laser and may be applied to vertical cavity surface emitting lasersof, for example, a 680-nm band (GaInP/AlGaInP active layer system).

The techniques (systems) used in the growth, lithography, etching,ashing and deposition in this embodiment are not limited to theabove-described techniques (systems), and any other techniques (systems)may be used so far as like effects can be achieved.

Example 2

In Example 2, a structural example of a vertical cavity surface emittinglaser array according to another embodiment than the array of Example 1constituted by applying the present invention is described. A differenceof Example 2 from Example 1 resides in that the second insulating layeris formed only in regions in contact with the metal material layer forwiring.

FIGS. 3 and 3A illustrate the vertical cavity surface emitting laserarray according to this embodiment. FIG. 3A is a cross-sectional viewtaken along line 3A-3A in FIG. 3.

In FIGS. 3 and 3A, a semiconductor layer 300, a metal material layer302, a first insulating layer 304, second insulating layer 306, anactive layer 308, a metal material layer 310 for wiring and an electrode312 are illustrated.

In the vertical cavity surface emitting laser array according to thisembodiment, the first insulating layer 304 is formed on thesemiconductor layer 100 and portions other than the top surface of mesastructure which is so formed that the DBR mirror layer is exposed.

The metal material layer 302 for heat dissipation is formed over thesemiconductor layer 300, on which the first insulating layer 304 isformed, so as to cover them including side portions of the active layer308. The second insulating layer 306 is formed only in regions incontact with the metal material layer 310 for wiring on the metalmaterial layer 302 for heat dissipation.

The production process of the vertical cavity surface emitting laserarray according to this embodiment will hereinafter be described.

FIGS. 4A to 4G are typical drawings illustrating the production processof the surface emitting laser array according to this embodiment.

In FIGS. 4A to 4G, an n-type GaAs substrate 400, a semiconductor epilayer 402, an active layer 404, a mesa structure 406, a first insulatinglayer 408, a metal material layer 410 for heat dissipation, a secondinsulating layer 412, a metal material layer 414 for wiring and anelectrode metal layer 216 are illustrated.

In this embodiment, the vertical cavity surface emitting laser array isproduced through the following steps.

First, as illustrated in FIG. 4A, the semiconductor epi layer 402 isgrown on the n-type GaAs substrate 400 through a buffer layer in thefollowing manner by an MOCVD system. More specifically, an n-typeAl_(0.9)Ga_(0.1)As/Al_(0.12)Ga_(0.88)AS-DBR mirror layer, an n-typeAl_(0.6)Ga_(0.4)As spacer layer, and a GaAs/Al_(0.3)Ga_(0.7)As-MQWactive layer 404 are successively grown. Further, a p-typeAl_(0.6)Ga_(0.4)As spacer layer, a p-type Al_(0.3)Ga_(0.7)As layer, ap-type Al_(0.9)Ga_(0.1)As/Al_(1.12)Ga_(0.88)AS-DBR mirror layer and ap-type GaAs contact layer are then successively grown.

As illustrated in FIG. 4B, the mesa structure 406 is then formed bymeans of lithographic and dry etching techniques so as to expose then-type Al_(0.9)Ga_(0.1)As/Al_(0.12)Ga_(0.88)AS-DBR mirror layer.

As illustrated in FIG. 4C, a first insulating layer (silicon oxide film)408 is then formed at portions other than the top surface of the mesastructure by means of CVD film-forming, lithographic and etchingtechniques.

As illustrated in FIG. 4D, a metal material (Ti/Au) layer 410 for heatdissipation is then formed to a thickness of 3 μm by means oflithographic and metal deposition techniques so as to cover side regionsof the active layer 404.

As illustrated in FIG. 4E, a second insulating layer 412 is then formedon portions other than the upper surface of the mesa structures by meansof CVD film-forming, lithographic and etching techniques.

As illustrated in FIG. 4F, a metal material (Ti/Au) layer 414 for wiringfor device-driving is then formed to a thickness of 1 μm on the secondinsulating layer by means of lithographic and metal depositiontechniques.

Thereafter, the substrate is dipped in a buffered hydrofluoric acid,whereby the second insulating layer is etched by using the metalmaterial layers 414 as a mask. In other words, regions of the secondinsulating layer which are not in contact with the second metal materiallayers are removed by the etching according to this process.

As illustrated in FIG. 4G, an electrode metal (AuGe/Au) layer 416 isthen formed on the n-type GaAs substrate 400 by means of a metaldeposition technique.

By the steps described above, the vertical cavity surface emitting laserarray in which the metal material layer for efficiently dissipating heatgenerated in the active layers of the surface emitting laser devices andthe metal material layer that is wiring for driving the surface emittinglaser device are individually formed can be obtained.

In particular, the second insulating layer is formed only in the regionsin contact with the metal material layer for wiring in this embodiment,whereby regions of the metal for heat dissipation covered with theinsulating layer with low thermal conductivity can be minimized, and soheat can be more efficiently dissipated.

Incidentally, a 4×4 vertical cavity surface emitting laser array havinga mesa diameter of 20 μm and a mesa pitch of 40 μm is formed in thisembodiment. In this embodiment, the metal material layer for heatdissipation having a thickness of 2.5 μm from the center of the activelayer is formed by deposition.

The thickness of the metal material layer for heat dissipation iscontrolled in such a manner that the height from the top of the mesastructure to the outermost surface of the metal material layer for heatdissipation is 2 μm or less. By taking such construction, the metalmaterial layer for wiring can be formed without disconnection.Incidentally, if the height from the top of the mesa structure to theoutermost surface of the metal material layer for heat dissipationexceeds 2 μm, the frequency of disconnection becomes high.

In an m×n (m and n: natural numbers exclusive of 0) vertical cavitysurface emitting laser array having a pitch of 80 μm or less betweensurface emitting laser devices according to this construction, thefollowing advantage can be obtained. More specifically, the metalmaterial layers for heat dissipation and for wiring are isolated fromeach other (a layered structure is taken with an insulating layerinserted between these layers), whereby the degree of freedom of wiringpattern can be increased. In addition, a narrow-pitch, two-dimensionalvertical cavity surface emitting laser array that can inhibitdisconnection and efficiently dissipate heat generated in active layerscan be produced.

Although the 850-nm band vertical cavity surface emitting laser has beendescribed in this embodiment, the present invention is not limited tothis laser and may be applied to vertical cavity surface emitting lasersof, for example, a 680-nm band (GaInP/AlGaInP active layer system).

The techniques (systems) used in the growth, lithography, etching,ashing and deposition in this embodiment are not limited to thedescribed techniques (systems), and any other techniques (systems) maybe used so far as like effects can be achieved.

Example 3

In Example 3, a structural example of an image forming apparatus havingthe vertical cavity surface emitting laser array according to thepresent invention is described.

FIGS. 5A and 5B illustrate structural drawings of an image formingapparatus of an electrophotographically recording system, in which thevertical cavity surface emitting laser array according to the presentinvention is mounted. FIG. 5A is a side elevation of the image formingapparatus, and FIG. 5B is a side elevation of the apparatus.

In FIGS. 5A and 5B, a photosensitive drum 500, a charger 502, adeveloper 504, a transfer charger 506, a fixer 508, a polygon mirror510, a motor 512, the vertical cavity surface emitting laser array 514,a reflection mirror 516, a collimator lens 520 and an f-θ lens 522 areillustrated.

In FIGS. 5A and 5B, the motor 512 rotationally drives the polygon mirror510. The polygon mirror 510 in this embodiment has six reflectionsurfaces. The vertical cavity surface emitting laser array 514 serves asa light source for recording. The vertical cavity surface emitting laserarray 514 is turned on or off by a laser driver (not illustrated)according to image signals.

Laser beams optically modulated in this manner are emitted toward thepolygon mirror 510 through the collimator lens 520 from the verticalcavity surface emitting laser array 514. The polygon mirror 510 isrotated in the direction of the arrow, and the laser beams outputtedfrom the vertical cavity surface emitting laser array 514 are reflectedto be deflected beams continuously varying the outgoing angle on thereflection surfaces of the polygon mirror 510 with the rotation of thepolygon mirror 510.

The reflected beams are subjected to compensation for distortion by thef-θ lens 522, exposed to the photosensitive drum 500 through thereflection mirror 516 and scanned in a main scanning direction.

At this time, an image of plural lines corresponding to the verticalcavity surface emitting laser array 514 is formed on the photosensitivedrum 500 in the main scanning direction by the reflection of the laserbeams on one surface of the polygon mirror 510. A 4×8 vertical cavitysurface emitting laser array 514 is used in this embodiment, and so animage of 4 lines is formed.

The photosensitive drum 500 is charged in advance by the charger 502 andis subjected to successive exposure by the scanning of the laser beamsto form an electrostatic latent image. The photosensitive drum 500 isrotated in the direction of the arrow, the electrostatic latent imageformed is developed by the developer 504, and a visible image developedis transferred to transfer paper (not illustrated) by the transfercharger 506.

The transfer paper, to which the visible image has been transferred, isconveyed to the fixer 508 and discharged out of the apparatus after thefixing.

Incidentally, a beam detection sensor (not illustrated; hereinafterreferred to as “BD sensor”) is arranged in the vicinity of ascan-starting position in the main scanning direction in a side portionof the photosensitive drum 500. The laser beams reflected on therespective reflection surfaces of the polygon mirror 510 are detected bythe BD sensor prior to the line scanning. The detected signals areinputted as scan-starting reference signals into a timing controller(not illustrated), and write-starting positions of scanning directionsof the respective lines are synchronized based on these signals.

Incidentally, the 4×8 vertical cavity surface emitting laser array isused in this embodiment. However, the present invention is not limitedto this laser array, and an m×n (m and n: natural numbers exclusive of0) vertical cavity surface emitting laser array may also be used.

As has been described above, the vertical cavity surface emitting laserarray according to the present invention is used in the image formingapparatus of the electrophotographically recording system, whereby animage forming apparatus capable of performing high-speed andhigh-definition printing can be obtained.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-048860, filed Feb. 28, 2007, which is hereby incorporated byreference herein in its entirety.

1. A surface emitting laser array comprising a plurality of surfaceemitting laser devices each including a semiconductor layer thatincludes a first reflection mirror, an active layer, a current confinedportion, and a second reflection mirror, the surface emitting laserarray further comprising: a first metal material layer for dissipatingheat formed through a first insulating layer on the semiconductor layer;and a second metal material layer for injecting current into the activelayer formed through a second insulating layer on the first metalmaterial layer, wherein the first metal material layer is commonlyshared by the plurality of the surface emitting laser devices, whereinthe first insulating layer is formed on the semiconductor layer excepton a laser emission port formed on an upper layer side of the secondreflection mirror, wherein the first metal material layer is formed onthe semiconductor layer including at least the active layer through thefirst insulating layer, and wherein the active layer is disposed at aposition lower than an upper surface of the first metal material layerand higher than a lower surface of the first metal material layer. 2.The surface emitting laser away according to claim 1, wherein the secondinsulating layer is formed only in a region in contact with the secondmetal material layer.
 3. The surface emitting laser array according toclaim 1, wherein the plurality of the surface emitting laser deviceshave a pitch therebetween of 80 μm or less.
 4. The surface emittinglaser array according to claim 1, wherein the surface emitting laserarray is incorporated in an image forming apparatus.